What genetically engineered machines (modified bacteria) should we build?

Dear everyone,

I'm part of a student team participating in the "international genetically engineered machine competition" ( http://www.igem.org ). During this year we will build modified bacteria, with the aim of doing something useful. Everything we build and all results will be open-source.

Our aim this year is not just to do science in our laboratory, but instead with an acute awareness of society, including continuous feedback on the ethical, legal and social issues (and if we can manage, public participation in the scientific process itself).

At the moment we are at square one: Idea Generation. During the next week, our team will brainstorm ideas and develop project candidates. But we also want to tap into highly engaged communities such as TED conversations, to collect interesting ideas for a "genetically engineered machine".

So here's my question: "Which genetically engineered machine (modified bacteria) should we build?" (what are the biggest problems that could be tackled / What are the most ingenious uses of modified bacteria )

Feb 26 2013:
Maybe customizable virus killers. Antiviral drugs could be huge. I don't know if that's even possible, I'm no biologist, but I think would change the world much like penicillin did over a hundred years ago.

Feb 26 2013:
Not exactly, read it very well and focus on this part:
Our Sporobeads can be used to purify water from heavy metal ions, toxins and plastic by expressing proteins on their surface that specifically bind such targets.
and I repeat the important part of this:

heavy metal ions, toxins and plastic
those are very limited pollutants in water, water purification is more complex than that, therefore my original comment states a bacteria that acts as a pig (can practically digest anything) in water, not a chicken (that will only feed on some limited organic and inorganic materials), pigs have an incredible digestive capacity to eat almost anything in front of them and properly dipoe of it, hence creating a bacteria that purifies water is more complex than simply removing some heavy metals and some organic materials, it requires a true feeder bacteria to acomplish that.

Feb 25 2013:
Bacteria that take a commonly found & bountiful product or substance, feed on it & produce a byproduct that can be used as fuel. Not a new idea, but perhaps something that could be improved upon. Made more efficient. Produced on mass & cheaply. Hydrogen production for example.

Feb 22 2013:
a bacteria which could produce human insulin and secret it. a totally not pathogenic bacteria. inject it to patients with diabetics. the bacterial could live in the gut and secret the insulin. well first you have to try it on mice.

How about bioluminescence for one? Maybe Luciferin (found in fireflies) could be modified to emit light for longer periods without deterioration, at a bigger scale and with a wider colour spectrum for lighting areas off-grid.

Just imagine a building constructed to mimic the natural air conditioning found in termite mounds using an array of tunnels and vents, lit by bioluminescent lighting, powered by sugar/ethanol fuel from modified/accelerated photosynthesis, and whose waste is digested in reed beds, or composted (not as yucky as you might think!).